Cutting tools, including cemented carbide cutting tools, have been used in both coated and uncoated conditions for machining various metals and alloys. In order to increase cutting tool wear resistance, performance and lifetime, one or more layers of refractory material have been applied to cutting tool surfaces. TiC, TiCN, TiN and/or Al2O3, for example, have been applied to cemented carbide substrates by chemical vapor deposition (CVD) and by physical vapor deposition (PVD). While effective in inhibiting wear and extending tool lifetime in a variety of applications, refractory coatings based on single or multi-layer constructions of the foregoing refractory materials have increasingly reached their performance limits, thereby calling for the development of new coating architectures for cutting tools.
In an effort to increase performance, some have tried to modify Al2O3. DE2736982 to Hillnhagen describes a ceramic matrix (e.g. alumina), into which a further material (e.g. ZrO2) is stored and the stored material has clearly distinct coefficients of thermal expansion producing a coating with very fine micro-cracks.
U.S. Pat. No. 4,702,970 to Sarin et al. and U.S. Pat. No. 4,749,629 to Sarin et al. describe a hard ceramic substrate coated with a ceramic coating having at least two phases. The first phase is a continuous oxide matrix layer of alumina, zirconia, or yttria. At least one discontinuous second or additional phase of oxides of aluminum, zirconium, or yttrium, or solid solutions thereof, is dispersed as discrete particles within the matrix layer. The additional phase material is different from the matrix material.
In Russell, W. C., Strandberg, C., “Wear Characteristics and Performance of Alumina-Zirconia CVD Coatings”, Int. J. of Refractory Metals & Hard Materials, 14 (1996) 51-58, the authors describe using various doped amounts of ZrO2 within an alumina matrix. Further, this article discloses a Ti layer adjacent the substrate followed by a pure alumina layer for adhesion followed by an Al2O3/ZrO2 coating.
U.S. Pat. No. 7,276,301 to Tsushima et al. discloses an α-type (Al,Zr)2O3 layer with a TiOy upper layer. The (Al,Zr)2O3 is deposited having a β-type crystal structure. Post coat heat treatment is described as a method of converting the (Al,Zr)2O3 an α-type crystal structure.
U.S. Pat. No. 7,597,511 to Tomita et al. discloses an aluminum oxide layer with α-type crystal structure and containing Zr. The Zr containing coating is claimed to have a particular crystallographic orientation where a defined Σ3 value is greater than 60%.